Signaling for reference picture resampling

ABSTRACT

A method, device, and non-transitory computer-readable medium for decoding an encoded video bitstream using at least one processor, including obtaining a coded picture from the encoded video bitstream; decoding the coded picture to generate a decoded picture; obtaining a first flag indicating whether reference picture resampling is enabled; obtaining a second flag indicating whether reference pictures have a constant reference picture size; obtaining a third flag indicating whether output pictures have a constant output picture size indicated in the encoded video bitstream; generating a reference picture by resampling the decoded picture to have the constant reference picture size, and storing the reference picture in a decoded picture buffer; and generating an output picture by resampling the decoded picture to have the constant output picture size, and outputting the output picture.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 17/243,019,filed Apr. 28, 2021, which is a continuation of U.S. patent applicationSer. No. 16/899,202, filed on Jun. 11, 2020, now U.S. Pat. No.11,032,548 issued Jun. 8, 2021, in the United States Patent & TrademarkOffice, which claims priority from 35 U.S.C. § 119 to U.S. ProvisionalApplication No. 62/865,955, filed on Jun. 24, 2019, in the United StatesPatent & Trademark Office, the disclosures of which are incorporatedherein by reference in their entireties.

FIELD

The disclosed subject matter relates to video coding and decoding, andmore specifically, to the signaling information relating to referencepicture resampling and adaptive resolution change.

BACKGROUND

Video coding and decoding using inter-picture prediction with motioncompensation has been known. Uncompressed digital video can consist of aseries of pictures, each picture having a spatial dimension of, forexample, 1920×1080 luminance samples and associated chrominance samples.The series of pictures can have a fixed or variable picture rate(informally also known as frame rate), of, for example 60 pictures persecond or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reducing aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding, some of which will be introducedbelow.

Historically, video encoders and decoders tended to operate on a givenpicture size that was, in most cases, defined and stayed constant for acoded video sequence (CVS), Group of Pictures (GOP), or a similarmulti-picture timeframe. For example, in MPEG-2, system designs areknown to change the horizontal resolution (and, thereby, the picturesize) dependent on factors such as activity of the scene, but only at Ipictures, hence typically for a GOP. The resampling of referencepictures for use of different resolutions within a CVS is known, forexample, from ITU-T Rec. H.263 Annex P. However, here the picture sizedoes not change, only the reference pictures are being resampled,resulting potentially in only parts of the picture canvas being used (incase of downsampling), or only parts of the scene being captured (incase of upsampling). Further, H.263 Annex Q allows the resampling of anindividual macroblock by a factor of two (in each dimension), upward ordownward. Again, the picture size remains the same. The size of amacroblock is fixed in H.263, and therefore does not need to besignaled.

Changes of picture size in predicted pictures became more mainstream inmodern video coding. For example, VP9 allows reference pictureresampling and change of resolution for a whole picture. Similarly,certain proposals made towards VVC (including, for example, Hendry, et.al, “On adaptive resolution change (ARC) for VVC”, Joint Video Teamdocument JVET-M0135-v1, Jan. 9-19, 2019, incorporated herein in itsentirety) allow for resampling of whole reference pictures todifferent—higher or lower—resolutions. In that document, differentcandidate resolutions are suggested to be coded in the sequenceparameter set and referred to by per-picture syntax elements in thepicture parameter set.

SUMMARY

In an embodiment, there is provided a method of decoding an encodedvideo bitstream using at least one processor, including obtaining acoded picture from the encoded video bitstream; decoding the codedpicture to generate a decoded picture; obtaining from the encoded videobitstream a first flag indicating whether reference picture resamplingis enabled; based on the first flag indicating that the referencepicture resampling is enabled, obtaining from the encoded videobitstream a second flag indicating whether reference pictures have aconstant reference picture size indicated in the encoded videobitstream; based on the first flag indicating that the reference pictureresampling is enabled, obtaining from the encoded video bitstream athird flag indicating whether output pictures have a constant outputpicture size indicated in the encoded video bitstream; based on thesecond flag indicating that the reference pictures have the constantreference picture size, generating a reference picture by resampling thedecoded picture to have the constant reference picture size, and storingthe reference picture in a decoded picture buffer; and based on thethird flag indicating that the output pictures have the constant outputpicture size, generating an output picture by resampling the decodedpicture to have the constant output picture size, and outputting theoutput picture.

In an embodiment, there is provided a device for decoding an encodedvideo bitstream, the device including at least one memory configured tostore program code; and at least one processor configured to read theprogram code and operate as instructed by the program code, the programcode including: first obtaining code configured to cause the at leastone processor to obtain a coded picture from the encoded videobitstream; decoding code configured to cause the at least one processorto decode the coded picture to generate a decoded picture; secondobtaining code configured to cause the at least one processor to obtainfrom the encoded video bitstream a first flag indicating whetherreference picture resampling is enabled; third obtaining code configuredto, based on the first flag indicating that the reference pictureresampling is enabled, cause the at least one processor to obtain fromthe encoded video bitstream a second flag indicating whether referencepictures have a constant reference picture size indicated in the encodedvideo bitstream; fourth obtaining code configured to, based on the firstflag indicating that the reference picture resampling is enabled, causethe at least one processor to obtain from the encoded video bitstream athird flag indicating whether output pictures have a constant outputpicture size indicated in the encoded video bitstream; first generatingcode configured to, based on the second flag indicating that thereference pictures have the constant reference picture size, cause theat least one processor to generate a reference picture by resampling thedecoded picture to have the constant reference picture size, and storethe reference picture in a decoded picture buffer; and second generatingcode configured to, based on the third flag indicating that the outputpictures have the constant output picture size, cause the at least oneprocessor to generate an output picture by resampling the decodedpicture to have the constant output picture size, and output the outputpicture.

In an embodiment, there is provided a non-transitory computer-readablemedium storing instructions, the instructions including: one or moreinstructions that, when executed by one or more processors of a devicefor decoding an encoded video bitstream, cause the one or moreprocessors to: obtain a coded picture from the encoded video bitstream;decode the coded picture to generate a decoded picture; obtain from theencoded video bitstream a first flag indicating whether referencepicture resampling is enabled; based on the first flag indicating thatthe reference picture resampling is enabled, obtain from the encodedvideo bitstream a second flag indicating whether reference pictures havea constant reference picture size indicated in the encoded videobitstream; based on the first flag indicating that the reference pictureresampling is enabled, obtain from the encoded video bitstream a thirdflag indicating whether output pictures have a constant output picturesize indicated in the encoded video bitstream; based on the second flagindicating that the reference pictures have the constant referencepicture size, generate a reference picture by resampling the decodedpicture to have the constant reference picture size, and store thereference picture in a decoded picture buffer; and based on the thirdflag indicating that the output pictures have the constant outputpicture size, generate an output picture by resampling the decodedpicture to have the constant output picture size, and output the outputpicture.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 7 is a flowchart of an example process for decoding an encodedvideo bitstream in accordance with an embodiment.

FIG. 8 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION

Embodiments disclosed herein may be used separately or combined in anyorder. Further, each of the methods (or embodiments), encoder, anddecoder may be implemented by processing circuitry (e.g., one or moreprocessors or one or more integrated circuits). In one example, the oneor more processors execute a program that is stored in a non-transitorycomputer-readable medium.

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. The system(100) may include at least two terminals (110-120) interconnected via anetwork (150). For unidirectional transmission of data, a first terminal(110) may code video data at a local location for transmission to theother terminal (120) via the network (150). The second terminal (120)may receive the coded video data of the other terminal from the network(150), decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals (130, 140) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (130, 140) may code video data captured at a locallocation for transmission to the other terminal via the network (150).Each terminal (130, 140) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 1, the terminals (110-140) may be illustrated as servers,personal computers and smart phones but the principles of the presentdisclosure may be not so limited. Embodiments of the present disclosurefind application with laptop computers, tablet computers, media playersand/or dedicated video conferencing equipment. The network (150)represents any number of networks that convey coded video data among theterminals (110-140), including for example wireline and/or wirelesscommunication networks. The communication network (150) may exchangedata in circuit-switched and/or packet-switched channels. Representativenetworks include telecommunications networks, local area networks, widearea networks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (150) may beimmaterial to the operation of the present disclosure unless explainedherein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that caninclude a video source (201), for example a digital camera, creating afor example uncompressed video sample stream (202). That sample stream(202), depicted as a bold line to emphasize a high data volume whencompared to encoded video bitstreams, can be processed by an encoder(203) coupled to the camera (201). The encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (204), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (205) for future use. One or morestreaming clients (206, 208) can access the streaming server (205) toretrieve copies (207, 209) of the encoded video bitstream (204). Aclient (206) can include a video decoder (210) which decodes theincoming copy of the encoded video bitstream (207) and creates anoutgoing video sample stream (211) that can be rendered on a display(212) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (204, 207, 209) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as Versatile Video Coding or VVC.The disclosed subject matter may be used in the context of VVC.

FIG. 3 may be a functional block diagram of a video decoder (210)according to an embodiment of the present disclosure.

A receiver (310) may receive one or more codec video sequences to bedecoded by the decoder (210); in the same or another embodiment, onecoded video sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (312), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (310) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (310) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween receiver (310) and entropy decoder/parser (320) (“parser”henceforth). When receiver (310) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer (315) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (315) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (210) may include a parser (320) to reconstructsymbols (321) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(210), and potentially information to control a rendering device such asa display (212) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 3. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (320) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameter corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures,sub-pictures, tiles, slices, bricks, macroblocks, Coding Tree Units(CTUs) Coding Units (CUs), blocks, Transform Units (TUs), PredictionUnits (PUs) and so forth. A tile may indicate a rectangular region ofCU/CTUs within a particular tile column and row in a picture. A brickmay indicate a rectangular region of CU/CTU rows within a particulartile. A slice may indicate one or more bricks of a picture, which arecontained in an NAL unit. A sub-picture may indicate an rectangularregion of one or more slices in a picture. The entropy decoder/parsermay also extract from the coded video sequence information such astransform coefficients, quantizer parameter values, motion vectors, andso forth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (315), so to create symbols(321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). The flow of such subgroup control information between theparser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder 210 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). It can output blockscomprising sample values, that can be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(358). The aggregator (355), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (352) has generatedto the output sample information as provided by the scaler/inversetransform unit (351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (321)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (356) as symbols (321) from theparser (320), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to the render device (212) as well as stored in the referencepicture memory for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (320)), the current reference picture(358) can become part of the reference picture buffer (357), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder 210 may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (310) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (210) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or SNR enhancementlayers, redundant slices, redundant pictures, forward error correctioncodes, and so on.

FIG. 4 may be a functional block diagram of a video encoder (203)according to an embodiment of the present disclosure.

The encoder (203) may receive video samples from a video source (201)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (203).

The video source (201) may provide the source video sequence to be codedby the encoder (203) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, ...) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (201) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (203) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more sample depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focusses on samples.

According to an embodiment, the encoder (203) may code and compress thepictures of the source video sequence into a coded video sequence (443)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (450). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller (450) as they may pertain to video encoder (203) optimizedfor a certain system design.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of an encoder (430)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (433) embedded in the encoder (203) that reconstructs thesymbols to create the sample data a (remote) decoder also would create(as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (434). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder (210), which has already been described in detail abovein conjunction with FIG. 3. Briefly referring also to FIG. 4, however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder (445) and parser (320) can be lossless, theentropy decoding parts of decoder (210), including channel (312),receiver (310), buffer (315), and parser (320) may not be fullyimplemented in local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focusses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

As part of its operation, the source coder (430) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (432) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (433) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (434). In this manner, the encoder (203) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new frame to be coded, the predictor (435)may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the video coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare it for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (430) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the encoder (203). Duringcoding, the controller (450) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by- block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (203) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The video coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

FIG. 5 illustrates an example of an encoder 500, according to anembodiment, and FIG. 6 illustrates illustrates an example of an decoder600 according to an embodiment. Referring to FIG. 5, encoder 500 mayinclude down-sampler 501, picture partitioner 502, dequantizer 503,entropy coder 504, in-loop filter 505, intra-predictor 506, decodedpicture buffer (DPB) 507, re-sampler 508, and inter predictor 509.Referring to FIG. 6, decoder 600 may include coded picture buffer 601,video syntax parser 602, dequantizer 603, in-loop filter 604, decodedpicture buffer 605, re-sampler 606, inter predictor 607, and intrapredictor 608.

In embodiments, one or more elements illustrated in FIG. 5 and/or FIG. 6may correspond to, or perform similar functions to, one or more elementsillustrated in FIG. 3 and/or FIG. 4.

In embodiments, for example the embodiments illustrated in FIGS. 5 and6, it is possible to change the picture width and height, on a perpicture granularity irrespective of the picture type. At the encoder500, the input image data may be down-sampled to the selected picturesize, using for example down-sampler 501, for the current pictureencoding. After the first input picture is encoded as intra-picture, thedecoded picture is stored in the DPB 507. When the consequent picture isdown-sampled with a different sampling ratio and encoded asinter-picture, the reference pictures in the DPB may be up-scaled ordown-scaled according the spatial ratio between the picture size of thereference and the current picture size, using for example re-sampler508.

At the decoder 600, the decoded picture may be stored in the DPB 605without resampling. However, the reference picture in the DPB 605 may beup-scaled or down-scaled in relation to the spatial ratio between thecurrently decoded picture and the reference, for example usingre-sampler 606, when used for motion compensation. The decoded picturemay be up-sampled to the original picture size or the desired outputpicture size, using for example up-sampler 609, when bumped out fordisplay. In motion estimation/compensation process, motion vectors maybe scaled in relation to picture size ratio as well as picture ordercount difference.

In embodiments, a reference picture resampling (RPR) scheme, as used forexample in the embodiments disclosed herein, may include support ofadaptive (decoded) picture resolution change within a coded videosequence, support of constant reference picture resolution forsimplification of motion compensation process, support of constantoutput picture resolution for guided display resolution, and support ofadaptive resampling modes, both with and without additional filtering.

In embodiments, in order to support the desired features for RPR andadaptive resolution change (ARC), a set of high-level syntaxmodifications ma be used.

For example, in embodiments, a minimum/maximum picture resolution may besignaled in a decoder parameter set (DPS) to facilitate capexchange/negotiation.

In embodiments, a flag indicating that RPR is enabled in a coded videosequence may be signaled in a sequence parameter set (SPS). Decodedpicture resolutions may be signaled in a table in an SPS. This table mayinclude a list of decoded picture sizes, which may be used by one ormore pictures in the coded video sequence.

In embodiments, a flag indicating that any reference picture has thesame spatial resolution, and the constant reference picture size may besignaled in an SPS. If the flag value is 1, any decoded picture in thecoded video sequence may be up-scaled by a re-sampling process, so thatany reference picture stored in DPB may have the same picture size withthe reference picture size, signaled in the SPS.

In embodiments, a flag indicating that any output picture has the samespatial resolution, and the constant output picture size may be signaledin an SPS. If the flag value is 1, any output picture in the coded videosequence may be up-scaled by a re-sampling process, so that anyoutputted picture may have the same picture size with the output picturesize, signalled in SPS.

In embodiments, an index indicating the decoded picture size from amongthe candidates signaled in an SPS may be signaled in a picture parameterset (PPS). This index may be used to facilitate cap exchange/negotiation

In embodiments, a flag indicating that motion vector scaling fortemporal motion vector prediction is disabled may be signaled in a PPS.If the flag value is 1, any temporal motion vector prediction may beprocessed without motion vector scaling.

In embodiments, a filter mode selection may be signaled in a PPS.

An example of a DPS syntax for signaling the embodiments discussed aboveis shown in Table 1 below:

TABLE 1 Descriptor dec_parameter_set_rbsp( ) { ...max_pic_width_in_luma_samples ue(v) max_pic_height_in_luma_samples ue(v)... }

In embodiments, max_pic_width_in_luma_samples may specify the maximumwidth of decoded pictures in units of luma samples in the bitstream.max_pic_width_in_luma_samples may not be equal to 0 and may be aninteger multiple of MinCbSizeY. The value ofmax_pic_width_in_luma_samples[i] may not be greater than the value ofmax_pic_width_in_luma_samples.

In embodiments, max_pic_height_in_luma_samples may specify the maximumheight of decoded pictures in units of luma samples.max_pic_height_in_luma_samples may not be equal to 0 and may be aninteger multiple of MinCbSizeY. The value ofmax_pic_height_in_luma_samples[i] may not be greater than the value ofmax_pic_height_in_luma_samples.

An example of an SPS syntax for signaling the embodiments discussedabove is shown in Table 2 below:

TABLE 2 Descriptor seq_parameter_set_rbsp( ) { ...reference_pic_resampling_flag u(1) if(reference_pic_resampling_flag) {num_dec_pic_size_in_luma_samples_minus1 ue(v) for( i = 0; i <=num_dec_pic_size_in_luma_samples_minus1; i++ ) {dec_pic_width_in_luma_samples[ i ] ue(v) dec_pic_height_in_luma_samples[i ] ue(v) } constant_ref_pic_size_flag u(1)if(constant_ref_pic_size_flag) {  reference_pic_width_in_luma_samplesue(v)  reference_pic_height_in_luma_samples ue(v) }constant_output_pic_size_flag u(1)  if(constant_output_pic_size_flag) {output_pic_width_in_luma_samples ue(v) output_pic_height_in_luma_samplesue(v) } } else {  pic_width_in_luma_samples ue(v) pic_height_in_luma_samples ue(v) } ... }

In embodiments, reference_pic_resampling_flag equal to 1 may specifythat the decoded picture size of a coded picture associated with the SPSmay or may not change within the coded video sequence.reference_pic_resampling_flag equal to 0 specifies that the decodedpicture size of a coded picture associated with the SPS may not changewithin the coded video sequence. When the value ofreference_pic_resampling_flag is equal to 1, one or more decoded picturesizes (dec_pic_width_in_luma samples[i], dec_pic_height_in_lumasamples[i]), which may be indicated and used by a coded picture withinthe coded video sequence, may be present, and a constant referencepicture size (reference_pic_width_in_luma_samples,reference_pic_height_in_luma_samples) and a constant output picture sizeoutput_pic_width_in_luma_samples, outputpic_height_in_luma_samples) arepresent, conditioned on the values of constant_ref_pic_size_present_flagand constant output_pic_size_present_flag, respectively.

In embodiments, constant ref_pic_size_flag equal 1 may specify thatreference_pic_width_in_luma_samples andreference_pic_height_in_luma_samples are present.

In embodiments, reference_pic_width_in_luma_samples may specify thewidth of the reference picture in units of luma samples.reference_pic_width_in_luma_samples may not be equal to 0. When notpresent, the value of reference_pic_width_in_luma_samples may beinferred to be equal to dec_pic_width_in_luma_samples[i].

In embodiments, reference_pic_height_in_luma_samples may specify theheight of the reference picture in units of luma samples.reference_pic_height_in_luma_samples may not be equal to 0. When notpresent, the value of reference_pic_height_in_luma_samples may beinferred to be equal to dec_pic_height_in_luma_samples[i].The size ofthe reference picture, stored in DPB, may be equal to the values ofreference_pic_width_in_luma_samples andreference_pic_height_in_luma_samples, when the value ofconstant_pic_size_present_flag is equal to 1. In this case, anyadditional resampling process may be not performed for motioncompensation.

In embodiments, constant_output_pic_size_flag equal 1 may specify thatoutputpic width in luma samples and output_pic_height_in_luma_samplesare present.

In embodiments, output_pic_width_in_luma_samples may specify the widthof the output picture in units of luma samples.output_pic_width_in_luma_samples shall not be equal to 0. When notpresent, the value of output_pic_width_in_luma_samples may be inferredto be equal to dec_pic_width_in_luma_samples[i].

In embodiments, output_pic_height_in_luma_samples may specify the heightof the output picture in units of luma samples.output_pic_height_in_luma_samples may not be equal to 0. When notpresent, the value of output_pic_height_in_luma_samples may be inferredto be equal to dec_pic_height_in_luma_samples[i]. The size of the outputpicture may be equal to the values of output_pic_width_in_luma_samplesand output_pic_height_in_luma_samples, when the value ofconstant_output_pic.

In embodiments, num_dec_pic_size_in_luma_samples_minus1 plus 1 mayspecify the number of the decoded picture size(dec_pic_width_in_luma_samples[i], dec_pic_height_in_luma_samples[i] inunits of luma samples in the coded video sequence.

In embodiments, decpic width in luma samples[i] may specify the i-thwidth of the decoded picture sizes in units of luma samples in the codedvideo sequence. dec_pic_width_in_luma_samples[i] may not be equal to 0and may be an integer multiple of MinCbSizeY.

In embodiments, dec_pic_height_in_luma_samples[i] may specify the i-thheight of the decoded picture sizes in units of luma samples in thecoded video sequence. dec_pic_height_in_luma_samples[i] may not be equalto 0 and may be an integer multiple of MinCbSizeY. The i-th decodedpicture size (dec_pic_width_in_luma_samples[i],dec_pic_height_in_luma_samples[i] may be equal to the decoded picturesize of the decoded picture in the coded video sequence.

An example of a PPS syntax for signaling the embodiments discussed aboveis shown in Table 3 below:

TABLE 3 Descriptor pic_parameter_set_rbsp( ) { ... if(reference_pic_resampling_flag) {  dec_pic_size_idx ue(v)disabling_motion_vector_scaling_flag u(1)  rpr_resampling_mode u(2)  }... }

In embodiments, dec_pic_size_idx may specify that the width of thedecoded picture shall be equal topic_width_in_luma_samples[dec_pic_size_idx] and the height of thedecoded picture shall be equal topic_height_in_luma_samples[dec_pic_size_idx].

In embodiments, disabling_motion_vector_scaling_flag equal 1 may specifythat a reference motion vector is used without scaling process dependenton POC values or spatial resolutions for temporal motion vectorprediction. disabling_motion_vector_scaling_flag equal 0 may specifythat a reference motion vector is used with or without scaling processdependent on POC values or spatial resolutions for temporal motionvector prediction.

In embodiments, rpr_resampling_mode equal 0 may indicate that theinterpolated pixels in a reference picture are not additionally filteredfor motion compensation when the resolution of the current picture isdifferent from the that of the reference picture. rpr_resampling_modeequal 1 may indicate that the interpolated pixels in a reference pictureare additionally filtered for motion compensation, when the resolutionof the current picture is different from the that of the referencepicture. rpr_resampling_mode equal 2 may indicate that the pixels in areference picture are filtered and interpolated for motion compensation,when the resolution of the current picture is different from the that ofthe reference picture. Other values may be reserved.

ARC may be included in the “baseline/main” profiles. Sub-profiling maybe used to remove them if not needed for certain application scenarios.Certain restrictions may be acceptable. In that regard, certain H.263+profiles and “recommended modes” (which pre-dated profiles) included arestriction for Annex P to be used only as “implicit factor of 4”, i.e.dyadic downsampling in both dimensions. That was enough to support faststart (get the I frame over quickly) in video conferencing.

In embodiments, all filtering can be done “on the fly” and there may beno, or only negligible, increases in memory bandwidth. As a result, itmay not be necessary to place ARC into exotic profiles.

Complex tables and such may not be meaningfully used in capabilityexchange, as it was argued in Marrakech in conjunction with JVET-M0135.The number of options may be simply too big to allow for meaningfulcross-vendor interoperability, assuming offer-answer and similarlimited-depth handshakes. To support ARC in a meaningful way in acapability exchange scenario, a handful of interop points may be used.For example: no ARC, ARC with implicit factor of 4, full ARC. As analternative, we could spec the required support for all ARC, and leavethe restrictions in bitstream complexity to higher level SDOs.

As for levels, as a condition of bitstream conformance in someembodiments, the sample count of an upsampled pictures must fit intolevel of bitstream no matter how much upsampling is signalled inbitstream, and that all samples must fit into the upsampled codedpicture. We note that this was not the case in H263+; there, it waspossible that certain samples were not present.

FIG. 7 is a flowchart is an example process 700 for decoding an encodedvideo bitstream in accordance with embodiments discussed above. In someimplementations, one or more process blocks of FIG. 7 may be performedby decoder 210 or decoder 600. In some implementations, one or moreprocess blocks of FIG. 7 may be performed by another device or a groupof devices separate from or including decoder 210 or decoder 600, suchas encoder 203 or encoder 500.

As shown in FIG. 7, process 700 may include obtaining a coded picturefrom the encoded video bitstream (block 701).

As further shown in FIG. 7, process 700 may include decoding the codedpicture to generate a decoded picture (block 702).

As further shown in FIG. 7, process 700 may include obtaining from theencoded video bitstream a first flag indicating whether referencepicture resampling is enabled (block 703). In embodiments, the firstflag may correspond to reference_pic_resampling_flag described above.

As further shown in FIG. 7, process 700 may include determining from thefirst flag whether reference picture resampling is enabled (block 704).If reference picture resampling is enabled (YES at block 704), process700 may proceed to block 705. In embodiments, if reference pictureresampling is not enabled, process 700 may decode the encoded videobitstream according to a different process.

As further shown in FIG. 7, process 700 may include obtaining from theencoded video bitstream a second flag indicating whether referencepictures have a constant reference picture size indicated in the encodedvideo bitstream, and a third flag indicating whether output pictureshave a constant output picture size indicated in the encoded videobitstream (block 705). In embodiments, the second flag may correspond tothe constant_ref_pic_size_flag described above, and the third flag maycorrespond to the constant_output_pic_size_flag described above.

As further shown in FIG. 7, process 700 may include determining whetherthe second flag indicates that the reference pictures have the constantreference picture size (block 706). If the reference pictures have theconstant reference picture size (YES at block 706), process 700 mayproceed to block 707 and then to block 708. If the reference pictures donot have the constant reference picture size (NO at block 706), process700 may proceed directly to block 708.

As further shown in FIG. 7, process 700 may include generating areference picture by resampling the decoded picture to have the constantreference picture size (block 707).

As further shown in FIG. 7, process 700 may include storing thereference picture in a decoded picture buffer (block 708). If block 707is not performed, the decoded picture may be stored as the referencepicture without resampling

As further shown in FIG. 7, process 700 may include determining whetherthe third flag indicates that the output pictures have the constantoutput picture size (block 709). If the output pictures have theconstant output picture size (YES at block 709), process 700 may proceedto block 710 and then to block 711. If the output pictures do not havethe constant output picture size (NO at block 709), process 700 mayproceed directly to block 711.

As further shown in FIG. 7, process 700 may include generating an outputpicture by resampling the decoded picture to have the constant outputpicture size (block 710).

As further shown in FIG. 7, process 700 may include outputting theoutput picture (block 711). If block 710 is not performed, the decodedpicture may be output as the output picture without resampling.

In embodiments, the first flag, the second flag, and the third flag maybe signaled in a sequence parameter set included in the encoded videobitstream.

In embodiments, process 700 may further include obtaining pictureresolution information from the encoded video bitstream, wherein thepicture resolution information indicates at least one from among amaximum picture resolution and a minimum picture resolution.

In embodiments, the picture resolution information may be signaled in adecoder parameter set included in the encoded video bitstream.

In embodiments, process 700 may further include obtaining a list ofpicture sizes from the encoded video bitstream.

In embodiments, process 700 may further include obtaining an indexindicating a picture size of the decoded picture within the list ofpicture sizes.

In embodiments, the list of picture sizes may be signaled in a sequenceparameter set included in the encoded video bitstream, and the index maybe signaled in a picture parameter set included in the encoded videobitstream.

In embodiments, process 700 may further include obtaining a fourth flagindicating whether motion vector scaling is enabled. In embodiments, thefourth flag may correspond to the disabling_motion_vector_scaling_flagdescribed above.

In embodiments, the fourth flag may be signaled in a picture parameterset included in the encoded video bitstream.

Although FIG. 7 shows example blocks of process 700, in someimplementations, process 700 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 7. Additionally, or alternatively, two or more of theblocks of process 700 may be performed in parallel.

Further, the proposed methods may be implemented by processing circuitry(e.g., one or more processors or one or more integrated circuits). Inone example, the one or more processors execute a program that is storedin a non-transitory computer-readable medium to perform one or more ofthe proposed methods.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 8 shows a computersystem 800 suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 8 for computer system 800 are exemplary innature and are not intended to suggest any limitation as to the scope ofuse or functionality of the computer software implementing embodimentsof the present disclosure. Neither should the configuration ofcomponents be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system 800.

Computer system 800 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 801, mouse 802, trackpad 803, touch screen 810and associated graphics adapter 850, data-glove 1204, joystick 805,microphone 806, scanner 807, camera 808.

Computer system 800 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 810, data-glove 1204, or joystick 805, but there can alsobe tactile feedback devices that do not serve as input devices), audiooutput devices (such as: speakers 809, headphones (not depicted)),visual output devices (such as screens 810 to include cathode ray tube(CRT) screens, liquid-crystal display (LCD) screens, plasma screens,organic light-emitting diode (OLED) screens, each with or withouttouch-screen input capability, each with or without tactile feedbackcapability—some of which may be capable to output two dimensional visualoutput or more than three dimensional output through means such asstereographic output; virtual-reality glasses (not depicted),holographic displays and smoke tanks (not depicted)), and printers (notdepicted).

Computer system 800 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW820 with CD/DVD or the like media 821, thumb-drive 822, removable harddrive or solid state drive 823, legacy magnetic media such as tape andfloppy disc (not depicted), specialized ROM/ASIC/PLD based devices suchas security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 800 can also include interface(s) to one or morecommunication networks (955). Networks can for example be wireless,wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include global systems formobile communications (GSM), third generation (3G), fourth generation(4G), fifth generation (5G), Long-Term Evolution (LTE), and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters (954) that attached to certain generalpurpose data ports or peripheral buses (949) (such as, for exampleuniversal serial bus (USB) ports of the computer system 800; others arecommonly integrated into the core of the computer system 800 byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). As an example, network 855 may be connectedto peripheral bus 849 using network interface 854. Using any of thesenetworks, computer system 800 can communicate with other entities. Suchcommunication can be uni-directional, receive only (for example,broadcast TV), uni-directional send-only (for example CANbus to certainCANbus devices), or bi-directional, for example to other computersystems using local or wide area digital networks. Certain protocols andprotocol stacks can be used on each of those networks and networkinterfaces (954) as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core 840 of thecomputer system 800.

The core 840 can include one or more Central Processing Units (CPU) 841,Graphics Processing Units (GPU) 842, specialized programmable processingunits in the form of Field Programmable Gate Areas (FPGA) 843, hardwareaccelerators 844 for certain tasks, and so forth. These devices, alongwith Read-only memory (ROM) 845, Random-access memory (RAM) 846,internal mass storage such as internal non-user accessible hard drives,solid-state drives (SSDs), and the like 847, may be connected through asystem bus 848. In some computer systems, the system bus 848 can beaccessible in the form of one or more physical plugs to enableextensions by additional CPUs, GPU, and the like. The peripheral devicescan be attached either directly to the core's system bus 848, or througha peripheral bus 849. Architectures for a peripheral bus includeperipheral component interconnect (PCI), USB, and the like.

CPUs 841, GPUs 842, FPGAs 843, and accelerators 844 can execute certaininstructions that, in combination, can make up the aforementionedcomputer code. That computer code can be stored in ROM 845 or RAM 846.Transitional data can be also be stored in RAM 846, whereas permanentdata can be stored for example, in the internal mass storage 847. Faststorage and retrieve to any of the memory devices can be enabled throughthe use of cache memory, that can be closely associated with one or moreCPU 841, GPU 842, mass storage 847, ROM 845, RAM 846, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture 800, and specifically the core 840 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 840 that are of non-transitorynature, such as core-internal mass storage 847 or ROM 845. The softwareimplementing various embodiments of the present disclosure can be storedin such devices and executed by core 840. A computer-readable medium caninclude one or more memory devices or chips, according to particularneeds. The software can cause the core 840 and specifically theprocessors therein (including CPU, GPU, FPGA, and the like) to executeparticular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 846and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 844), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of decoding an encoded video bitstreamusing at least one processor, the method comprising: obtaining a codedpicture from the encoded video bitstream; obtaining from the encodedvideo bitstream a first flag indicating whether reference pictureresampling is enabled; based on the first flag indicating that thereference picture resampling is enabled, obtaining a second flagindicating whether motion vector scaling is disabled; based ondetermining that the motion vector scaling is disabled, decoding thecoded picture using the reference picture resampling and using areference motion vector without scaling.
 2. The method of claim 1,wherein the first flag is signaled in a sequence parameter set includedin the encoded video bitstream.
 3. The method of claim 1, wherein thesecond flag is signaled in a picture parameter set included in theencoded video bitstream.
 4. The method of claim 1, wherein based ondetermining that the motion vector scaling is not disabled, decoding thecoded picture using the reference picture resampling and using a scaledreference motion vector.
 5. The method of claim 1, further comprisingobtaining picture resolution information from the encoded videobitstream, wherein the picture resolution information indicates at leastone from among a maximum picture resolution and a minimum pictureresolution.
 6. The method of claim 5, wherein the picture resolutioninformation is signaled in a decoder parameter set included in theencoded video bitstream.
 7. The method of claim 1, further comprisingobtaining a list of picture sizes from the encoded video bitstream. 8.The method of claim 7, further comprising obtaining an index indicatinga picture size of the decoded picture within the list of picture sizes.9. The method of claim 8, wherein the list of picture sizes is signaledin a sequence parameter set included in the encoded video bitstream, andwherein the index is signaled in a picture parameter set included in theencoded video bitstream.
 10. A device for decoding an encoded videobitstream, the device comprising: at least one memory configured tostore program code; and at least one processor configured to read theprogram code and operate as instructed by the program code, the programcode including: first obtaining code configured to cause the at leastone processor to obtain a coded picture from the encoded videobitstream; second obtaining code configured to cause the at least oneprocessor to obtain, from the encoded video bitstream, a first flagindicating whether reference picture resampling is enabled; thirdobtaining code configured to cause the at least one processor to, basedon the first flag indicating that the reference picture resampling isenabled, obtain a second flag indicating whether motion vector scalingis disabled; and decoding code configured to cause the at least oneprocessor to, based on the motion vector scaling being disabled, decodethe coded picture using the reference picture resampling and using areference motion vector without scaling.
 11. The device of claim 10,wherein the first flag is signaled in a sequence parameter set includedin the encoded video bitstream.
 12. The device of claim 10, wherein thesecond flag is signaled in a picture parameter set included in theencoded video bitstream.
 13. The device of claim 10, wherein based ondetermining that the motion vector scaling is not disabled, decoding thecoded picture using the reference picture resampling and using a scaledreference motion vector.
 14. The device of claim 10, further comprisingobtaining picture resolution information from the encoded videobitstream, wherein the picture resolution information indicates at leastone from among a maximum picture resolution and a minimum pictureresolution.
 15. The device of claim 14, wherein the picture resolutioninformation is signaled in a decoder parameter set included in theencoded video bitstream.
 16. The device of claim 10, further comprisingobtaining a list of picture sizes from the encoded video bitstream. 17.The device of claim 16, further comprising obtaining an index indicatinga picture size of the decoded picture within the list of picture sizes.18. The device of claim 17, wherein the list of picture sizes issignaled in a sequence parameter set included in the encoded videobitstream, and wherein the index is signaled in a picture parameter setincluded in the encoded video bitstream.
 19. A non-transitorycomputer-readable medium storing instructions, the instructionscomprising: one or more instructions that, when executed by one or moreprocessors of a device for decoding an encoded video bitstream, causethe one or more processors to: obtain a coded picture from the encodedvideo bitstream; obtain from the encoded video bitstream a first flagindicating whether reference picture resampling is enabled; based on thefirst flag indicating that the reference picture resampling is enabled,obtain a second flag indicating whether motion vector scaling isdisabled; and based on the motion vector scaling being disabled, decodethe coded picture using the reference picture resampling and using areference motion vector without scaling.
 20. The non-transitorycomputer-readable medium of claim 19, wherein based on determining thatthe motion vector scaling is not disabled, decoding the coded pictureusing the reference picture resampling and using a scaled referencemotion vector